It is well documented that cyclopropenoid fatty acids (CPFA) included in diets with various mycotoxins or other carcinogens greatly enhance the induction of liver cell cancer in rainbow trout. These fatty acids occur in a variety of seed oils consumed by man and animals. The mechanism for this cocarcinogenic action remains unexplained. The basic objective of this project is to examine the possibility that the cocarcinogenic properties of CPFA are related to structural modifications of cellular membranes. In the proposed project rainbow trout will be raised on diets containing various levels of CPFA. A 41,500 molecular weight protein stimulated in trout by CPFA exposure will be purified to homogeneity and characterized by electrophoretic, ultracentrifugal and immunological methods. The location of the 41,500 molecular weight protein will be assessed in cell organelles by ferritin-labelled antibodies and electron microscopic immunochemistry. In addition, the effects of CPFA on the synthesis of membrane and cytosolic proteins will be investigated in isolated trout hepatocytes.